The present invention relates to an electrophotography apparatus, such as a printer, a copy machine, etc. More particularly, the present invention relates to an electrophotography apparatus which is capable of producing a highly reliable picture of high quality by preventing image defects, such as image deformation, without undesirably affecting the positioning accuracy of each printing unit inside the apparatus, when the apparatus is typically placed on a desk or the floor.
In accordance with conventional techniques, the positioning of each structural member in an electrophotography apparatus is ensured by the side plates (or members attached to the side plates) that are disposed perpendicular to the central rotational axes of the respective printing units within the electrophotography apparatus. Further, in order to set up the electrophotography apparatus on a desk or the floor, two legs are attached under one of the side plates and one leg is attached under the other one, or two pairs of legs are attached under each of the respective side plates.
Also, in accordance with the above conventional techniques, the positioning accuracy of each of the devices which make up the electrophotography apparatus depends on the flatness of the surface of the desk or the floor on which the electrophotography apparatus is set up. Generally, an accuracy in the order of 0.1 mm is required for the positioning of each device within the electrophotography apparatus. However, since the surface of a typical desk or a floor sometimes has an irregularity of a few mm, when the electrophotography apparatus is placed on such a surface, the electrophotography apparatus receives a reaction force from that surface, due to its own weight, and the side plates of the electrophotography apparatus, which also ensure the positioning of each device within the electrophotography apparatus, are distorted, and this makes the accurate positioning of each device difficult. If the positioning of each device in the electrophotography apparatus is not accurately maintained, an image produced by the apparatus may be disordered, and a defect in the image, such as an image deformation, may result due to the variations in operational speed of each device, the slipping in an image transfer process, etc. Particularly, in the printing of a multi-colored image, an image is created by precisely superimposing toner images of different colors on an intermediate transfer device in the electrophotography apparatus. Therefore, a higher positioning accuracy is required for each device for the printing of a multi-color image in comparison with the printing of a monochromatic image. If the positioning accuracy of each device is not sufficient, the desired color will not be obtained, due to a misalignment in the superimposition of the color images, and a defect in the image occurs. In order to solve the above problem, it has been suggested as a countermeasure to increase the stiffness of the side plates, for example, by thickening the side plates, so that a distortion in the side plates does not occur even if they receive a reaction force from the surface on which the electrophotography apparatus is placed. However, this countermeasure cannot be adopted because it results in a high production cost and an increase in the weight of the apparatus.
So, a construction has been proposed in which two legs are fitted under one of the side plates of the electrophotography apparatus and one leg is fitted under the other of the side plates. Accordingly, three legs are provided to support the electrophotography apparatus. By use of those three legs, the whole electrophotography apparatus is firmly supported, reclines even if the electrophotography apparatus is placed on a surface with a certain degree of irregularity, and with this arrangement, a distortion does not occur in the side plates. This is because a plane containing three points is uniquely determined.
Further, it is possible to provide an arrangement of the legs of the electrophotography apparatus, in which, although two pairs of legs are attached under the two side plates, respectively, one of the legs is used for adjusting the vertical position of the electrophotography apparatus. That is, this one leg is used to adjust the resting point implemented by this leg, as opposed to the three points implemented by the other three legs, to a plane determined by the three points.
However, in the case where three legs are used, the placement of the electrophotography apparatus is unstable relative to changes in the center of gravity of the electrophotography apparatus. The more the electrophotography apparatus is downsized, the larger will be the portion including devices, such as a developing device, in which toner powder is enclosed, a device which encloses recording media, such as sheets of paper, and so on, whose weight changes according to its history of use, becomes. This influences the degree of change in the center of gravity. Here, with a view toward reducing the fabrication cost, it is desirable to select a material of low cost for the side plates with function to position each device in the electrophotography apparatus, such that the material has as low a stiffness as possible, but has a sufficient stiffness to support the electrophotography apparatus. However, in the case where three legs are attached under the side plates, since the weight of the apparatus is concentrated on a particular one of the three legs, in response to a change in the position of the center of gravity, such as explained above, a distortion occurs in the side plates with low stiffness, and the positioning of each device in the apparatus gets out of order, which in turn causes a defect in the image.
Further, in the electrophotography apparatus, it is necessary to replace expendable components, such as a developing device in which toner powder is enclosed, periodically or according to its stage of use. Also, in order to reduce the price of the electrophotography apparatus, it is desirable for a general user to perform some maintenance tasks on the apparatus, rather than have the maker or seller perform the maintenance tasks. However, as mentioned above, since the setting-up state of the apparatus is not stable due to the support of the apparatus by three legs, if a user applies a part of his weight onto the apparatus, for example, by pressing the top surface of the apparatus with his hand, when he replaces an expendable component, the apparatus may suddenly shift, which causes a discomfort to him. This problem becomes more remarkable as the size or weight of the apparatus becomes more reduced.
On the other hand, in the case where four legs are attached under the electrophotography apparatus, since the setting-up state of the apparatus is stable, the above problem does not occur in response to a change in the center of gravity, or even if a general user replaces an expendable component. However, in adopting this conventional technique, it is necessary to use one of the four legs for the height adjustment of the apparatus. Therefore, when such an electrophotography apparatus is purchased and is set up, it is required to adjust the height of the one leg, corresponding with the surface of the desk or floor on which the apparatus is to be set up. Furthermore, since movement of the apparatus to another location becomes easier with the downsizing or the weight reduction of the electrophotography apparatus, such movement of the apparatus is frequently performed after the initial set-up of the apparatus. However, since the above-discussed adjustment of the apparatus is difficult for a general user to perform, the maker or seller of the apparatus usually implements this adjustment, and this has been a contentious subject from the point of view of reducing the price of the electrophotography apparatus.